As per Navathe “pleaf to denote the order for leaf nodes, which we define as being the maximum number of data pointers in a leaf node.”
Also see this for reference https://gateoverflow.in/269367/b-tree-self-doubt
As per question only one order is mentioned hence we take Pleaf also as 8 and therefore 8 keys are present in each leaf node.
Ceil(5500/8) = ceil(687.5) = 688 --> Level 4 (5500 divided by keys per node)
ceil(688/8) = ceil(86) = 86 --> Level 3 (here we are dividing by 8 and not 7 because block pointer are 8 which takes us to next level)
ceil(86/8) = ceil(10.75) = 11 -->Level 2
ceil(11/8) = ceil(1.375) = 2 --> Level 1
ceil(2/8) = ceil(0.25) = 1 --> Level 0
Minimum number of nodes = 688 + 86 +11 +2 +1 = 788
Total nodes = 788